Does a ceiling need to be replaced if it gets wet?

Replace the drywall if the wet area exceeds one square foot or sags. Same call if it reads above 17 percent on a moisture meter after 48 hours of drying. Smaller stains with dry drywall behind them get primed (Kilz) and painted. Sagging always means replace. Gypsum loses structural integrity once saturated and won't recover. In Horry County, if framing or trusses are involved, you need a permit before repair. Painting over a brown spot without metering moisture traps water in the cavity. Mold seeds within 24-48 hours at our coastal dew points. Pull insulation back, check the topside, and replace any drywall that crumbles under thumb pressure.